A convincing body of evidence has emerged that demonstrates that airborne ultra-fine particles -also known as nanoparticles - have important consequences on human health and the environment. In this project, we will characterize the composition of these complex pollutants, with attention focused on halocarbons and persistent free radicals (PFRs). Nanoparticles are produced in copious quantities by combustion and thermal processes, and once produced, can impact environmental and health issues in two critically important ways. First, they can act as pollutants directly, and secondly, they can promote the production of other airborne -> pollutants. We have discovered that transiton metal-containing nanparticles can convert molecular pollutants to chemisorbed PFRs via redox processes and these PFRs are important in formation of other pollutants and the instrinsic toxicity of nanoparticles. We will prepare size selected nanoparticles with metal oxide cores to serve as surrogates for combustion-generated ultrafine particulate (UFP) matter. We will study the structure and chemical state of metals in nanoparticles using x-ray spectroscopy, NMR spectroscopy, TEM, as well as other traditional analytical techniques. We will study reaction mechanisms and kinetics that occur on nanoparticle surfaces using in situ x-ray absorption near edge structure spectroscopy and related methods. NMR studies will be performed to elucidate the structure of organic fraction of carbonaceous nanoparticles, as well as their interactions with trace metals that can produce and stabilize reactive radicals. The x-ray methods will be used to characterize the inorganic fraction of the particulate matter, as well as the organic components which exist at its interface. Conversely, the NMR methods will be used to characterize the organic fraction, as well as the interactions with inorganic dopants. We will also compare the structure of the well-defined surrogate nanoparticles with the more complex nanoparticles generated in combustion sources, using the same methods mentioned above (x-ray, NMR, infrared, UV/VIS, etc), and this will permit rigorous evaluation of the surrogates, as well as adjustments which optimize how the surrogates mimic the complex combustion generated particulate matter. This project includes materials chemistry, analytical chemistry, spectroscopy, and chemical kinetics, and such a multipronged approach will serve to identify and ameliorate the problems that arise because of the interactions of ultrafine particulate matter with the environment.